Advancements in communication technologies have permitted the creation and popularization of usage of cellular communication systems. The infrastructures of such communication systems have been installed throughout large geographical areas, and cellular communications are permitted by users within the areas encompassed by the cellular infrastructure.
The network infrastructure of a cellular communication system includes a plurality of spaced-apart radio base stations positioned at spaced intervals about a geographical area to be encompassed by the cellular system. Because the plurality of radio base stations are positioned at spaced intervals throughout the geographic area, communication signals, both downlink signals generated by a radio base station and uplink signals generated by a mobile terminal, need only be of only relatively low power levels to effectuate communications between a mobile terminal and a radio base station.
A significant advantage inherent of a cellular communication system is the ability to "re-use" the frequencies allocated to the cellular communication system. Because the communication signals are of relatively low power levels, the same frequencies can be allocated for communications in different ones of the cells of the communication system. That is to say, the same frequency can be used concurrently at a plurality of locations throughout the geographical area encompassed by the cellular communication system to permit a plurality of different communications between a plurality of different users to be concurrently effectuated.
The cells in which communications are effectuated at the same frequencies must be carefully selected so that concurrent generation of communication signals in the various cells do not interfere significantly with one another. If the frequencies are re-used at locations which are too close to one another, interference between the concurrently-transmitted signals on the same frequencies might result.
As usage of cellular communication systems have increased, capacity problems have, however, sometimes been evidenced. Proposals have been set forth to provide the various manners by which to increase the communication capacity of a cellular communication system.
Proposals have been set forth, for instance, to utilize adaptive antennas capable of creating directional antenna beam patterns. Base stations conventionally utilize antennas which form wide, non-changeable antenna lobes of, e.g., 120.degree. or 360.degree.. A base station transmits downlink signals to mobile stations and receives uplink signals from the mobile stations within the area encompassed by the antenna lobe. In contrast, an adaptive antenna is capable of forming a directional antenna beam pattern which encompasses an area smaller than the area typically encompassed by the antenna lobe formed by the antenna of a conventional base station. By utilizing antenna apparatus capable of forming directional antenna beam patterns, it is possible to increase the capacity of communications in either of at least two manners.
The frequency re-use distance can be decreased as the use of a directional antenna permits better suppression of unwanted signals from interfering with the transmission of desired communication signals. By decreasing the re-use distance, the frequencies available to the cellular communication system are used more frequently.
Capacity can also be increased by forming two or more non-overlapping antenna beam patterns within a single cell, thereby to permit concurrent communications to two or more mobile terminals within a single cell at the same frequency.
Frequency planning procedures are carried out to assign frequencies to the cells defined in the cellular communication system. In a frequency planning procedure for a conventional cellular communication system in which base stations have antenna apparatus which generate only single antenna patterns, traffic behavior in the cells need not be considered. Viz., communication signals communicated between the base station and the mobile terminal is distributed throughout the entire cell. Therefore, traffic behavior in the cell need not be taken into account when frequency planning procedures are undertaken. However, if the base stations instead utilize antenna apparatus capable of generating directional antenna beam patterns, traffic distribution must be considered when frequency planning procedures are undertaken.
As existing frequency planning procedures generally do not take into account traffic behavior and distribution, such existing frequency planning procedures shall be unable to adequately allocate frequencies in an optimal manner.
It is in light of this background information related to cellular communication systems and frequency planning procedures therefor that the significant improvements of the present invention have evolved.